Re^2: The value of pattern match variable $&

[spiritway]

IIRC, there is also a big performance hit, if any of these appear anywhere in your program.

[ikegami]

Regexps without captures are faster than regexps with captures. Using any of those three variables causes all regexps in that interpreter instance (similiar to "in that process") to behave as if they had captures. That slows down all regexps without captures.